Commonly used processes for the preparation of aromatic amines comprise two process stages: the aromatic hydrocarbon is first nitrated and then the nitrated aromatic hydrocarbon is hydrogenated to form the corresponding amine compound. Such processes have the drawback that they are energy and time consuming, require large amounts of reactants, and result in the production of considerable amounts of undesired by-products which need to be removed.
Accordingly there still remains a need for a process to produce aromatic amines directly from aromatic hydrocarbons resulting in a high yield and/or a substantially complete conversion.
Therefore, the present invention has the objective to provide a process for efficiently preparing aromatic amines, in particular aniline with high selectivity. A process with sufficiently high selectivity will improve the operating efficiency of the overall process by reducing the amount of unwanted end-products produced, allowing the process to be used on an industrial basis.
The process of the present invention is advantageous in its simplicity, use of operation, low capital and operating costs. The process can be run at a relatively low conversion of the feed hydrocarbon to the desired product due to the selectivity achieved. Selectivity is the amount of desired product divided by the total of all (desired and by-products) products. It will be appreciated that a process that runs at enhanced selectivity is highly advantageous even though the conversion may be low.
The selectivity achieved with the present process permits operation of the process at a relative low conversion, i.e. a change from the conventional objective of achieving the highest possible conversion. A substantial economic benefit is realised on an industrial scale even from increase in selectivity, which is achieved by the present invention, since the process retains and recycles a relative high percentage of unreacted aromatic hydrocarbon and ammonia.
The amount of unreacted aromatic hydrocarbon will depend on the percent per-pass conversion of the reactant aromatic hydrocarbon entering the ammoxidation reactor which is converted to products. Those skilled in the art will appreciate that factors such as specific choice of catalyst, specific operating temperature and the like can be adjusted to have the reactor operate at a desired conversion of the reactant aromatic hydrocarbon.
At lower operating conversion, there will be a greater amount of unreacted aromatic hydrocarbon and unreacted ammonia circulating in the process.
According to one embodiment of the present invention a process is provided for the production of aromatic amines by reacting an aromatic hydrocarbon with ammonia at a temperature of less than 500.degree. C. and a pressure of less than 10 bara in the presence of a catalyst comprising at least one metal selected from the group consisting of the transition elements, lanthanides and actinides.
According to another embodiment of the present invention, the process of the present invention allows to recycle a high percentage of unreacted aromatic hydrocarbon and ammonia (FIG. 1).
According to a preferred embodiment of the present invention, the aromatic hydrocarbon reacts with ammonia in the presence of an oxygen-containing gas.
More direct methods for the preparation of aromatic amines from aromatic hydrocarbons have been described in the prior art.
CA-A-553988 concerns a one-step process for the production of aromatic amines. In one embodiment a mixture of benzene, ammonia and oxygen is contacted in the vapour phase with a platinum catalyst at a temperature of about 1000.degree. C. In another embodiment, a mixture of benzene and ammonia is contacted in the vapour phase with a reducible metal oxide at a temperature of about 100 to 1000IC.
GB-A-1463997 describes a process for the amination of an aromatic compound which is miscible with ammonia comprising reacting said compound with ammonia at an elevated temperature and at a superatmospheric pressure in the presence of a doped conditioned nickel/nickel oxide/zirconium catalyst system.
In GB-A-1327494 a process is described for converting aromatic compounds and ammonia to aromatic amines in the presence of a prereduced and conditioned nickel/nickel oxide catalyst composition at a temperature in the range of 150 to 500.degree. C. and at a pressure in the range of 10 to 1000 atmospheres.
U.S. Pat. No. 2,948,755 discloses the preparation of aromatic amines by reacting an aromatic compound such as benzene with anhydrous ammonia in the presence of a group VI-B metal compound and a promoter consisting of an easily reducible metallic oxide at a temperature in the range from about 200 to 600.degree. C.
JP-A 06/293715 describes a process for aminating and/or cyanating an aromatic compound in the presence of ammonia using a catalyst carrying a Group VIII-element. In an example a Fe-silica catalyst is used for amination of benzene at 400.degree. C. The conversion rate of benzene was 0.85% and the selectivity rate for aniline was 97.3%.
None of the cited prior art documents disclose the features of the present process nor do these documents suggest the benefits associated with the process of the present invention.